NRLF 


EXCHANGE 


A  NEW  TYPE  OF  REDUCTOR  AND 

ITS  APPLICATION   TO  THE   DETERMINATION 

OF  IRON  AND  OF  VANADIUM. 


DISSERTATION 

Submitted  in  Partial  Fulfillment  of  the  Requirements 

for  the  Degree  of  Doctor  of  Philosophy  in 

the  Faculty  of  Pure  Science  in 

Columbia  University. 


BY 

JAMES  M.  HENDEL,  Litt.B. 

NEW  YORK  CITY 
1922 


A  NEW  TYPE  OF  REDUCTOR  AND 

ITS  APPLICATION  TO  THE   DETERMINATION 

OF  IRON  AND  OF  VANADIUM. 


DISSERTATION 

Submitted  in  Partial  Fulfillment  of  the  Requirements 

for  the  Degree  of  Doctor  of  Philosophy  in 

the  Faculty  of  Pure  Science  in 

Columbia  University. 


BY 

JAMES  M.  HENDEL,  Litt.B. 

NEW  YORK  CITY 
1922 


DEDICATED  TO  MY  FATHER 


478723 


It  gives  the  author  much  pleasure  to  acknowl- 
edge his  indebtedness  to  Professor  H.  T.  Beans  for 
his  open-minded,  scientific  attitude,  for  his  stimulat- 
ing criticism,  and  for  his  valued  advice  given 
throughout  the  course  of  this  work. 


In  any  analysis  where  an  oxidimetric  titration  is  em- 
ployed, it  is  essential  that  the  reducing  agent  be  one  which  is 
oxidized  to  a  chemical  entity  not  affected  by  the  titrating  fluid, 
and  that  the  excess  of  the  reducing  agent  be  completely  and 
easily  removable.  These  conditions  are  not  entirely  fulfilled 
by  some  of  the  more  common  reducing  agents.  It  is  well 
known  that  hydrogen  sulfide,  in  reducing,  is  converted  into 
substances  of  undefined  composition  titrable  by  permanganate 
solution ;  and  that  long-continued  boiling  in  a  stream  of  car- 
bon dioxide  is  necessary  to  ensure  complete  removal  of  the 
excess  hydrogen  sulfide.  A  recent  article  published  by  Lun- 
dell  and  Knowles1  gives  a  more  complete  account  of  the  errors 
and  difficulties  involved  in  the  use  of  hydrogen  sulfide.  Sulfur 
dioxide  solutions  and  alkali  sulfites,  unless  freshly  prepared, 
usually  contain  other  oxidizable  substances  not  removable  by 
boiling.2  The  reduction  with  sulfur  dioxide  requires  a  chloride 
solution  for  rapid  reaction,  which  necessitates  either  the  use 
of  "preventive  solution,"  as  in  the  Zimmermann-Reinhardt 
method  for  iron,  or  the  use  of  dichromate  with  an  external  in- 
dicator,neither  of  which  methods  is  comparable  in  precision 
with  a  permanganate  titration  in  sulfate  solution.  The  use  of 
this  gas  in  the  reduction  of  iron  solutions  is  further  compli- 
cated by  the  fact,  shown  by  Wardlaw  and  Clews,3  that  ferrous 
chloride,  in  the  presence  of  hydrochloric  acid,  is  oxidized  by 
sulfur  dioxide  in  accordance  with  the  equation  : 

4FeCl2  +  SO2  +  4HC1  ^  4FeCl3  +  2H2O  +  S, 
the  reaction  producing  a  maximum  of  ferric  ion  of  about  9  per 
cent.  The  possibility  of  the  sulfur  thus  formed  being  con- 
verted into  polythionates  by  excess  sulfur  dioxide  casts  fur- 
ther doubt  on  the  advisability  of  using-  this  gas.  Finally,  with 
this  gas,  as  with  hydrogen  sulfide,  boiling  in  a  current  of  car- 
bon dioxide  is  required  to  expel  the  excess,  which  process  re- 
quires considerable  time. 

From  the  viewpoint  of  the  conditions  above  stated,  hydro- 
gen suggests  itself  as  the  reducing  agent  par  excellence.  It 
is  oxidized  to  a  definite  entity,  hydrogen  ion,  which  is  not  titra- 
ble by  permanganate.  It  can  be  easily  and  completely  re- 


moved ;  in  fact  its  slight  solubility  at  room  temperature  pre- 
cludes the  need  for  its  removal.  Moreover  the  reaction  be- 
tween permanganate  and  hydrogen,  in  the  absence  of  a  cata- 
lyst, is  too  slow  to  affect  the  end  point  in  a  permanganate 
titration. 

To  use  hydrogen  effectively  as  a  reducing  agent,  a  cata- 
lyst is  necessary.  It  has  been  found  that  ferric  sulfate  solu- 
tions can  be  reduced  quantitatively  merely  by  bubbling  the  gas 
into  the  solution  in  which  is  immersed  a  platinized  platinum 
gauze.  It  is  not  necessary  to  bubble  the  gas  over  the  gauze ; 
it  is  only  necessary  to  saturate  the  solution  with  hydrogen  and 
then  to  bring  the  solution  into  contact  with  the  gauze ;  bub- 
bling the  gas  into  the  solution  serves  to  accomplish  both  these 
objectives.  To  make  the  process  more  efficient,  a  reductor  has 
been  devised  on  the  baffle-plate  principle,  as  shown  in  Figure 


•     FIC.I 

I.  It  consists  essentially  of  a  capillary  tube  (bore  1  mm.) 
which  passes  through  the  center  of  two  pieces  of  platinized 
platinum  gauze  which  are  held  in  place  by  small  supports  of 
glass  fused  to  the  glass  capillary.  The  dimensions  and  rela- 
tive positions  of  the  two  gauzes  are  determined  largely  by  con- 
venience, volume  of  solution,  size  of  flask,  etc.,  always  keeping 

8      ' 


in  mind  the  fact  that  the  speed  of  reduction  increases  with  in- 
crease in  the  total  surface  of  catalyst.  One  reductor  was  made 
with  a  lower  gauze  2.25  X  2.50  cm.  attached  0.5  cm.  from  the 
end  of  the  capillary,  with  an  upper  gauze  3.5  X  4  cm.  attached 
3  cm.  above  the  lower  gauze  and  bent  so  as  to  imprison  the 
gas  bubbles  leaving  the  lower  gauze ;  at  the  upper  gauze  the 
small  bubbles  coalesce  to  a  single  large  bubble  which,  on  es- 
caping, tilts  the  gauze  and  stirs  the  solution  very  effectively. 
Another  reductor  was  made  with  three  gauzes,  of  about  the 
same  total  surface  as  the  above,  arranged,  each  with  an  up- 
ward tilt,  so  that  every  bubble  came  in  contact  with  each 
gauze.  No  difference  in  speed  of  reduction  was  apparent. 

The  gauzes  were  plated  with  platinum  black  by  electrol- 
ysis of  chorplatinic  acid  at  3  volts  and  0.6  amperes,  then  elec- 
trolyzed  in  dilute  sulfuric  acid  for  an  hour  to  clean  the  gauze 
and  to  saturate  it  with  hydrogen.  For  a  total  surface  of  32  sq. 
cm.,  a  deposit  of  from  0.1  to  0.3  grams  of  platinum  was  found 
to  be  sufficient.  The  activity  of  all  reductors  w>as  found  to  in- 
crease with  use.  Three  different  reductors  were  used  for  about 
100  determinations  each,  with  an  average  reduction  period  of 
1.5  hours,  and  have  as  yet  shown  no  signs  of  decreased  activ- 
ity. When  palladium  black  was  used,  the  speed  of  reduction 
was  increased,  but  no  other  effect  w'as  noticeable.  For  most 
purposes,  platinum  black  should  be  effective  enough.  The  re- 
ductors, when  not  in  use,  should  be  kept  in  distilled  water,  and 
in  general,  given  the  same  careful  treatment  as  an  hydrogen 
electrode,  to  prevent  "poisoning." 

The  object  of  this  work  is  to  apply  the  hydrogen  reduc- 
tion process  to  the  determination  of  iron  in  ores  and  rocks. 
Since  titanium  and  vanadium  are  usually  associated  with  iron 
in  these  natural  products,  the  effect  of  the  reductor  on  both 
these  elements  must  also  be  ascertained.  The  effect  of  the  re- 
ductor on  vanadium  having  been  found,  it  was  decided  to  ap- 
ply the  method  to  the  determination  of  vanadium  in  steels. 

Preparation  of  Materials. 

Ferric  alum  (Kahlbaum's)  was  recrystallized  twice.  A 
solution  of  it  was  made  up  containing  10  g.  of  iron  per  liter 
with  20  c.c.  of  18  M  sulfuric  acid  per  liter  added  to  prevent 


hydrolysis.  The  iron  value  was  determined  by  careful  reduc- 
tion with  a  zinc  reductor  and  titration  with  standard  perman- 
ganate. 

Titanium  dioxide  (Kahlbaum's)  was  dissolved  in  excess 
hydrofluoric  acid,  a  solution  of  potassium-hydrogen-fluoride 
added,  the  crystals  of  potassium  titanifluoride  collected  and  re- 
crystallized  from  hydrofluoric  acid  solution.4  A  solution  con- 
taining 1.6  g.  of  titanium  per  liter  was  made  up  by  weighing 
out  the  requisite  amount  of  pure  dry  (110°)  salt,  treating  with 
sulfuric  acid  in  a  platinum  dish,  fuming  to  get  rid  of  all  fluo- 
ride, then  diluting  with  the  required  amount  of  water  to  make 
1M  sulfuric  acid.  The  titanium  content  was  checked  by  care- 
fully evaporating  a  known  volume  of  solution. 

Ammonium  vanadate  (Merck's)  was  recrystallized,  dis- 
solved in  hot  water,  made  just  acid  to  litmus  with  sulfuric 
acid,  cooled  and  filtered.  The  resulting  solution  of  vanadic 
acid  was  standardized  by  evaporating  known  volumes,  igniting 
and  weighing  the  residue  as  vanadium  pentoxide.  It  contain- 
ed 0.46  g.  of  vanadium  per  liter. 

Potassium  dichromate  was  recrystallized,  then  dissolved 
in  acidified  (sulfuric  acid)  water  to  make  a  solution  contain- 
ing about  15  g.  of  chromium  per  liter.  As  needed,  portions  of 
this  solution  were  diluted  to  produce  solutions  of  a  more  con- 
venient concentration.  The  chromium  content  was  deter- 
mined by  ferrous  sulfate-permanganate  titrations. 

Permanganate  solutions  were  usually  about  0.013  Molar 
and  0.003  Molar  (for  vanadium  titrations),  standardized  with 
Bureau  of  Standards  sodium  oxalate.  The  standard  ferrous 
sulfate  solution  contained  30  g.  of  ferrous  sulfate  heptahy- 
drate  and  50  c.c.  of  concentrated  sulfuric  acid  per  liter. 

The  hydrogen  used  was  taken  from  a  tank,  purified  by 
passing  it  successively  through  neutral  permanganate  solution, 
cotton  wool  ,distilled  water,  and  finally  cotton  wool;  it  was 
then  led  through  black  rubber  tubing  directly  to  the  glass 
capillary  of  the  reductor.  Before  using,  each  day,  the  "dead 
space"  in  the  gas  train  was  flushed  out  with  a  stream  of  hydro- 
gen for  from  10  to  15  minutes. 

10 


The  Determination  of  Iron 

Solutions  containing  0.1  g.  iron  as  ferric  sulfate  in  vol- 
umes of  from  100  to  150  c.c.  have  been  reduced  quantitatively 
under  a  variety  of  conditions.  Whether  the  solution  be  hot  or 
cold,  strongly  or  weakly  acid,  complete  reduction  can  be  ob- 
tained if  it  be  maintained  for  a  long  enough  period.  The  time 
required  has  been  found  to  depend  chiefly  on  the  size  of  re- 
ductor,  rate  of  bubbling,  temperature,  and  hydrogen  ion  con- 
centration. No  attempt  has  been  made  to  determine  the  mini- 
mum dimensions  of  the  reductor;  a  gauze  32  sq.  cm.  in  size 
usually  reduces  0.1  g.  of  iron  in  one  hour,  a  gauze  62  sq.  cm. 
in  size  requiring  only  three-quarters  of  an  hour.  The  rate  of 
bubbling  has  usually  been  regulated  so  as  to  stir  the  solution 
thoroughly ;  the  reduction  period  could  undoubtedly  be  de- 
creased by  more  rapid  bubbling,  without  danger  either  of  los- 
ing the  solution  or  of  wasting  the  gas.  Increase  in  tempera- 
ture, except  in  weakly  acid  solutions  where  it  promoted  hy- 
drolysis, decreased  the  reduction  time.  The  usual  procedure 
(designated  as  "hot,  cool"  in  Table  I)  has  been  to  start  the 
heating  at  the  same  time  as  the  reduction,  continuing  both 
processes  until  the  hot  solution  showed1  no  color  of  ferric  ion, 
then  cooling,  either  naturally,  or  more  rapidly  by  immersing 
the  flask  in  cold  water,  still  maintaining  the  reduction,  until 
room  temperature  was  reached.  Solutions  colorless  at  20°  and 
apparently  containing  no  ferric  ion  have  occasionally  shown 
incomplete  reduction ;  solutions,  colorless  while  hot,  have  al- 
ways shown  complete  reduction ;  therefore  to  ensure  complete 
reduction  ,the  solutions  have  been  reduced  until  colorless  at 
80°-90°  then  cooled  to  20°  for  titration.  The  time  required 
for  reduction  was  found  to  increase  with  the  acidity.  Solu- 
tions just  acid  to  litmus  and  similar  solutions  containing  in 
addition  3  c.c.  of  phosphoric  acid  (85  per  cent.)  in  volumes  of 
100  to  150  c.c.  have  been  reduced  at  20°  in  one  hour.  Even 
solutions  in  3  Molar  sulfuric  acid  have  been  completely  re- 
duced, with  or  without  heating,  in  one  hour.  But  as  a  rule,  an 
acidity  greater  than  0.5  M  sulfuric  acid  increased  the  reduc- 
tion period  to  more  than  one  hour.  In  the  absence  of  condi- 
tions requiring  a  higher  acidity,  the  concentration  of  sulfuric 
acid  for  the  reduction  should  be  0.5  Molar  or  less. 

11 


No. 


TABLE   I. 

Temp.         Time        Zn.  R. 
c.c. 

22.79 


34.22 


34.04 


H.R. 


Diff. 


Molar 

Min. 

18 

.05      20° 

60 

19 

.10      20° 

60 

18a 

.03      20° 

70 

19a 

.10)     20° 

80 

33f 

1.7     hot,  cool2 

60 

33g 

1.7      "   " 

140 

44a 

.5      "   " 

120 

45 

.5      "   " 

60 

46 

.5      "   " 

80 

51 

.7      "   " 

60 

51a 

.7      "   " 

60 

52 

.7      "   " 

160 

52a 

.7 

90 

53 

.7      "   " 

75 

53a 

.7      "  •' 

80 

54 

.7      "   " 

90 

54a 

7      «   tt 

70 

57 

1.5O) 

75 

57a 

1.4(i)    «   « 

90 

58 

1.5(0    "   " 

80 

58a 

L4(i)    «   « 

90 

c.c. 

c.c. 

22.84 

+.05 

22.86 

+.07 

22.75 

—.04 

22.80 

+.01 

34.26 

+.04 

34.23 

+.01 

34.16 

-.06 

34.19 

—.03 

34.24 

+.02 

34.04 

0 

" 

0 

u 

0 

34.05 

+.01 

34.05 

+.01 

34.06 

+.02 

34.05 

+.01 

34.10 

+.05 

34.03 

-.01 

34.03 

—.01 

33.97 

—.07 

34.06 

+.02 

Note  1:    Contains  3  c.c.  85%  H3PO4  in  addition  to  stated  amount  of 

H2S04. 
Note  2:    Solutions  were  reduced  hot  till  colorless,  then  cooled  to  20° 

while  reduction  was  maintained. 

This  table  is  representative  of  the  results  obtained  with 
the  above  reduction  process.  The  lettered  numbers  refer  to 
the  same  solutions  as  the  corresponding  numbers  unlettered. 
In  every  case,  the  same  amount  of  iron  (0.1  g.)  was  taken, 
the  different  titers  resulting  from  the  use  of  different  per- 
manganate solutions.  The  average  difference  between  the  two 
methods  is  less  than  one  part  per  thousand. 

Titanium 

The  effect  of  the  hydrogen  reductor  on  titanic  sulfate  solu- 
tions was  studied.  Previous  investigators  (Denham5,  Tele- 
tow6,  Diethelm7,  Eggert8)  have  found  it  impossible  to  com- 
pletely reduce  titanic  ion  to  titanous  ion  by  means  of  hydrogen 
and  platinized  platinum;  the  formation  of  titanous  ion  was 


12 


favored  by  increasing  the  hydrogen  pressure  and  also  by  in- 
creasing the  acidity,  but  increased  temperature  favored  the  for- 
mation of  titanic  ion.  A  maximum  reduction  of  61  per  cent, 
was  found  by  Eggert  using  a  0.21  N  titanic  sulfate  solution, 
2  N  with  respect  to  sulfuric  acid,  at  14°,  although  by  elec- 
trolytic reduction,  Diethelm  secured  100  per  cent,  reduction  of 
a  0.25  Molar  titanic  sulfate  solution  in  an  acid  concentration 
of  0.657  Molar  sulfuric  acid  and  99.9  per  cent,  reduction  in  a 
0.560  Molar  hydrochloric  acid  solution.  The  results  listed  in 
Table  II  show  a  maximum  reduction  of  71%.  In  experiments 
2,  2a,  3,  3a,  no  attempt  was  made  to  prevent  reoxidation  by 
the  air  or  by  the  oxygen  dissolved  in  the  water  used  for  wash- 
ing the  reductor. 

TABLE   II. 

* 

Titanic  Sulfate  Solutions. 

No.          H2SO4  Temp.  Time  Vol.  Ti  taken              % 

Molar  Min.  c.c.  Grams  Reduced 

2  1.4  20°               60  130  .0999            70.93 
2a                1.8  20°              60  100  .0999            71.20 

3  .7  20°  150  130  .1004  70.82 
3a                 .5             20°               60             175             .1004  66.0 

4  1.6  20°  120  130  .0400  27.1  (O 

5  1.6  hot  120  130  .0400  19.7C1) 

6  3.2  hot  90  130  .0800  29.5C1) 

Note  1:    Kept  in  atmosphere  of  H2 ;  boiled  H2O  used  for  washing. 

Solutions  containing  a  fixed  amount  of  ferric  alum  (0.1  g. 
of  iron)  and  varying  amounts  of  titanic  sulfate  were  reduced 
under  the  various  conditions  stated  in  Table  III.  It  may  be 
observed  from  this  table,  that  iron  can  be  successfully  deter- 
mined in  the  presence  of  0.0064  g.  of  Ti  provided  the  acidity 
be  less  than  0.5  M  sulfuric  acid.  For  acidities  equal  to  or 
greater  than  this,  the  presence  of  Ti  in  greater  amounts  than 
0.0032  g.  may  cause  high  values  for  the  iron  content. 


13 


TABLE  III. 

10  c.c.  Ferric  Alum  Solution  with  Varying  Amounts  of  Ti. 

No.  H2S°4  Time          Ti  Zn.R.  H.R. 

Molar          Temp.  Min.        Grams  c.c.  c.c. 

4b  .1                20°  60           .0016  22.791  2278 

5c  .15        hot,  cool  75           .0032  "  22.79 

6c  .3                20°  60           .0048  "  22.74 

7  .4  hot,  cool  60           .0064  "  22.80 
7a  .5               20°  60           .0064  "  23.17 

8  .5  hot,  cool  90           .0080  "  23.31 
5d  1.0               20°  70           .0032  32.S62  32.82 
4e  .8          hot,  cool  75           .0032  "  32.91 
6d  .3          hot,  cool  75           .0048  "  32.81 
7d  .3               20°  60           .0064  "  32.84 
7b  .4          hot,  cool  75           .0064  "  32.82 
8b  .7          hot,  cool  60           .0080  "  32.93 

15  .1  20°  60           .0160  "  32.86 

16  .1  20*  70           .0160  "  33.00* 
Note  1:  KMnO4  Solution  B,  1  c.c.  =  0.00517  g.  iron. 

Note  2:  KMnO4  Solution  C,  1  c.c.  =  0.003585  g.  iron. 

Note  3:  Reduced  solution  was  colorless. 

It  is  desirable,  however,  to  extend  the  above  limits,  both 
as  to  acidity  and  to  titanium  content.  With  the  latter  object 
in  view,  ferric  and  titanic  sulfate  solutions  were  reduced  after 
making  the  acid  concentration  0.06  M  sulfuric  acid  and  boiling 
to  precipitate  titanium  as  titanium  dioxide ;  in  every  experi- 
ment the  iron  value  proved  to  be  too  low.  It  was  then  decided 
to  take  advantage  of  the  extreme  sensitivity  of  titanous  ion 
and  comparative  stability  of  ferrous  ion  in  acid  solution 
toward  atmospheric  oxidation.9  After  reduction,  oxygen  from 
a  tank,  or  purified  air  was  bubbled  into  the  cooled  solution  of 
ferrous  and  titanous  ions  without  the  reductor.  Five  or  ten 
minutes  of  bubbling  with  a  moderately  fast  current  of  air 
usually  sufficed  to  reoxidize  all  titanous  ion  without  affecting 
ferrous  ion.  By  means  of  this  expedient,  0.1  g.  of  iron  was 
successfully  determined  in  the  presence  of  from  0.02  to  0.08  g. 
of  titanium  in  solutions  of  acidity  ranging  from  0.1  to  3.0  M 
sulfuric  acid.  In  all  cases,  the  reduction  was  carried  out  at 
20°,  the  violet  color  of  titanous  ion  indicating  when  the  iron 
was  entirely  reduced.  Absence  of  this  color  did  not  warrant 
the  conclusion  that  no  titanic  ion  had  been  reduced,  as  may  be 
seen  from  experiments  16d  and  18a  in  Table  IV. 

14 


TABLE   IV. 

Reduction  of  10  c.c.  Ferric  Alum  with  Varying  Amounts  of  Ti  and 
Subsequent  Reoxidation  of  Ti  by  Air  or  O2. 
Temperature  =  20°,   volume  100-150  c.c. 
Theoretical  Actual 


Ti      H2S04 

Time 

Time  for      Fe  titer 

titer 

No. 

Grams    Molar 

Min. 

Reoxidation         c.c. 

c.c.        Remarks 

15b 

.0160          .5 

60 

O2    2  min.        32.86 

32.80 

16b 

.5 

60 

O2    2  min. 

32.90 

ISc 

1.0 

70 

O2    2  m'm. 

32.78  Faint  violet 

16c 

1.0 

60 

none 

32.89  Colorless 

15d 

1.5 

75 

O2    3  min.        32.82 

32.84 

16d 

1.5 

60 

none 

32.95  Colorless 

15e 

2.0 

60 

O2    3  min. 

32.80  Violet  tinge 

16e 

2.0 

60 

O2    3  min. 

32.86 

6h 

.0208        1.5 

75 

none            32.86 

32.82  Colorless 

6i 

2.0 

60 

none            32.82 

34.7    Reduced  warm, 

violet  tinge 

7h 

.0224       2.0 

75 

O2    6  min 

32.87  Colorless 

7i 

.0224       3.0 

60 

O2    6  min. 

32.76 

18 

.0320         .15 

60 

O2    2  min.        32.86 

32.89  Violet  tinge 

19 

.15 

60 

O2    3  min. 

32.86        "        " 

20 

.15 

60 

none 

32.86 

18a 

.6 

60 

none 

33.15  Colorless 

19a 

.6 

90 

O2    6  min.        32.82 

32.81  Violet  tinge 

20a 

.6 

75 

O2    3  min. 

33.46  Violet  tinge 

18b 

.6 

60 

O2    6  min. 

32.75  Colorless 

19b 

.6 

60 

O2    6  min. 

32.79  Violet 

20b 

.6 

60 

O2    6  min. 

32.88  Colorless 

18c 

1.0 

75 

Air  10  min. 

32.79  Faint  violet 

19c 

1.0 

80 

Air  15  min. 

32.75       "        " 

20c 

1.0 

75 

Air    5  min. 

32.82       "        " 

18d 

2.0 

60 

Air  10  min. 

32.74       " 

19d 

1.9 

60 

Air   5  min. 

32.77 

18e 

2.5 

80 

Air   5  min. 

32.92 

19e 

2.5 

90 

Air  10  min. 

32.82 

20d 

2.5 

60 

none 

35.17  Violet 

20e 

3.0 

60 

Air  10  min. 

32.83 

21 

.0798         .4 

60 

Air   5  min. 

32.85 

22 

.4 

60 

Air  10  min. 

32.86        " 

21a 

.9 

60 

Air  10  min. 

32.76  Colorless 

23 

1.5 

60 

Air  10  min. 

32.82  Faint  violet 

21b 

2.0 

60 

Air  13  min. 

32.80 

23a 

2.5 

75 

Air  13  min. 

32.84  Violet 

22a 

3.0 

60 

Air  10  min. 

32.84 

22c 

3.0 

70 

O2    4  min.        34.22 

34.26 

22d 

3.0 

150 

O2  13  min. 

34.24  Deep  violet 

15 


Vanadium 

Since  iron  ores  may  contain  from  0.01  to  0.10  per  cent,  of 
vanadium,  it  is  necessary  to  consider  the  effect  of  the  hydro- 
gen reductor  on  this  element.  While  it  may  be  permissible  in 
technical  ore  analyses  to  neglect  such  small  amounts  of  vana- 
dium, from  the  view-point  of  the  precise  analyst,  however,  it 
is  desirable  to  ascertain*  definitely  the  extent  of  the  reduction 
undergone  by  vanadium. 

Experiments  with  the  reductor  on  vanadic  acid  solutions 
showed  variable  reduction,  depending  on  acidity,  temperature, 
and  concentration  of  vanadate  ion.  From  many  and  various 
experiments,  it  was  concluded  that : 

(1)  complete  reduction  to  tervalent  vanadium  cannot  be  at- 
tained with  the  vanad'ate  solutions  ordinarily  encountered  in 
analytical  work ; 

(2)  solutions  just  acid,  at  20°  lead  to  reduction  to  tetravalent 
vanadium  but  if  heated  tend  to  go  to  tervalent  vanadium ; 

(3)  solutions  with  0.5  to  1.0  M  sulfuric  acid  lead  to  reduction 
to  tetravalent  vanadium  whether  at  20°  or  higher  tempera- 
tures ; 

(4)  long-continued  reduction  at  any  temperature  and  even  in 
6  M  sulfuric  acid  leads  to  reduction  to  a  lower  stage  than 
tetravalence. 

Solutions  were  now  made  up  to  contain  0.1  g.  of  iron,  0  to 
0.003  g.  of  titanium  and  0.002  g.  of  vanadium,  representing  the 
relative  amounts  of  iron  and  titanium  ordinarily  encountered 
in  iron  ores,  but  with  a  vanadium-iron  ratio  twenty  times  that 
usually  met  with.  A  method  worked  out  for  such  mixtures 
should  surely  meet  the  situation  likely  to  occur  in  analytical 
practice. 

Since  the  hydrogen  reductor  method  gives  the  total  con- 
tent of  iron  plus  vanadium,  a  separate  procedure  is  necessary 
to  determine  the  correction  for  vanadium.  For  this  purpose, 
the  method  of  Campagne10  was  selected  as  the  one  best  "dove- 
tailing" with  the  proposed  procedure  for  dissolving  the  ore. 
Accordingly,  to  the  hot  "synthetic  ore"  solution,  about  20  c.c. 
in  volume,  was  added  potassium  permanganate  solution  in  ex- 

16 


cess,  and  the  pink  color  destroyed  by  boiling.  Then  30  c.c. 
of  concentrated  hydrochloric  acid  (13  M)  were  added,  and 
the  solution  evaporated  to  a  syrup ;  10  c.c.  of  sulfuric  acid 
(9M)  were  now  added,  the  solution  taken  down  to  dense  fumes 
of  sulfur  trioxide,  cooled,  diluted  with  50  c.c.  of  water  and 
again  taken  down  to  dense  fumes.  Two  evaporations  are 
necessary  to  ensure  the  formation  o£  tetravalent  vanadium, 
since  hydrochloric  acid  reduces  vanadate  to  a  mixture  of 
tetravalent  and  tervalent  vanadium.11  After  the  second  fum- 
ing, the  residue  was  cooled,  treated  with  50  c.c.  of  water,  heat- 
ed till  solution  was  effected,  diluted  to  150  to  170  c.c.,  cooled 
to  20°  and  titrated  with  0.013  M  permanganate.  This  titration 
gave  the  vanadium  content  plus  a  small  color  "blank."  The 
titrated  solution  was  then  reduced  with  hydrogen  at  20°  until 
colorless,  heated  to  about  90°  for  fifteen  minutes  to  ensure 
complete  reduction  of  ferric  ion,  then  cooled  rapidly  (fifteen 
minutes)  to  20° ;  at  this  point  the  reductor  was  removed  and 
the  solution  titrated  with  0.013  M  permanganate.  In  a  few 
cases,  in  order  to  remove  any  titanous  ion  that  may  have  been 
formed,  air  was  passed  into  the  cool  solution  for  from  5  to  10 
minutes  before  the  titration  was  made.  This  second  titration 
gave  the  iron  and  vanadium  content  plus  the  same  color 
"blank"  as  above;  the  difference  between  the  two  titrations 
gave  the  iron  content.  A  "blank"  containing  everything  but 
vanadium  wias  carried  along  with  the  ore  solutions  and  titrated 
to  get  the  color  "blank"  to  be  applied  to  all  the  vanadium 
titers.  It  is  essential  to  fume  strongly  to  ensure  complete  re- 
moval of  hydrochloric  acid,  otherwise  the  "blank"  varies  from 
0.10  to  0.20  c.c.  of  0.013  M  permanganate,  0.10  c.c.  being  the 
usual  value  found. 

In  Table  V  are  listed  the  results  of  the  above  procedure 
with  "synthetic  ore"  solutions.  It  may  be  noted  that  the 
Campagne  method  occasionally  yields  high  values  for  vana- 
dium, which  causes  correspondingly  low  values  for  iron.  In 
the  aggregate,  however,  the  amount  of  vanadium  found  con- 
curs well  with  that  taken ;  while  the  iron  conte'nt  as  found  by 
the  hydrogen  reductor  checks  that  found  by  the  zinc  reductor 
within  1.5  parts  per  thousand. 

17 


TABLE   V. 


Theoretical 

Ti  content          V  taken 

V  found  C        Fe  titer 

Fe  titer  H 

No. 

Grams             Grams 

Grams                c.c. 

c.c. 

1 

none                 .0018 

.0020                26.71 

26.49 

2 

II                                                           .4 

ii 

26.62 

3 

"                       " 

.0019 

26.57 

4 

"                       " 

.0015 

26.65 

5 

.0032 

.0017 



6 

»t                      « 

.0021 

26.69 

7 

H 

.0020 

26.781 

8 

«                .      » 

.0019 

26.67 

9 

i<                      « 

.0021 

.... 

10 

«i                      K 

.0018 

.... 

11 

i<                      « 

.0019 

12 

none 



26.61 

13 

" 

" 

26.80 

14 

.0032 

.0016 

.... 

15 

"                       " 

.0017                26.72 

26.831 

16 

<i                       a 

.0016 

26.672 

Note  1:    Air  for  5  minutes  to  reoxidise  titanous  ion. 
Note  2:    Air  for  10  minutes  to  reoxidise  titanous  ion. 

Theoretical  Fe  titer  is  result  of  three  determinations  by  Zn  reductor. 
Average  of  14  determinations  of  V  by   Campagne  method  =  .0018  ± 

.00017  g. 

Average  of  11  determinations  by  H  reductor  =  26.67  ±  .07  c.c. 
Corresponds  in  an  average  ore  to  53.34%  Fe  ±  .14%  as  against  53.42 

by  Zn  R. 

The  above  conditions  for  the  reduction  with  hydrogen 
were  necessitated  bythe  fact  that  long-continued  heating  leads 
to  the  formation  of  tervalent  vanadium.  It  has  been  shown 
that,  under  the  conditions  prescribed  above,  the  uncertainty 
attending  the  reduction  of  vanadate  ion  has  no  great  effect  on 
the  determination  of  iron,  even  though  the  vanadium-iron  ratio 
be  twenty  times  that  ordinarily  encountered  in  iron  ores.  With 
a  view  to  making  the  method  more  elastic,  without  sacrificing 
safety,  it  was  decided  to  reduce  the  ferric  ion  and  vanadate 
ion  in  the  hot  solution,  then  to  reoxidize  to  tetravalence  any 
tervalent  vanadium  that  may  be  formed  and  to  titrate  ferrous 
ion  plus  tetravalent  vanadium  as  above. 

Contrary  to  the  widely  prevalent  idea  that  ferrous  salts 
in  acid  solution  are  easily  oxidized  by  air,  it  has  been  found 

18 


that  bubbling  air  into  hot  solutions  of  ferrous  sulfate  has  little 
oxidizing  effect  on  ferrous  ion.  Baskerville  and  Stevenson12 
found  that  the  passage  of  air  for  three  hours  or  more  into  fer- 
rous sulfate  solutions  at  room  temperatures  has  no  appreciable 
effect  on  ferrous  ion,  while  at  temperatures  slightly  below  the 
boiling  point  of  the  solution,  the  amount  of  oxidation  was  only 
2  per  cent,  in  acid  solutions  and  5  per  cent,  in  neutral  solutions. 
Table  VI  shows  some  results  obtained  with  solutions  contain- 
ing 0.06  g.  of  ferrous  iron  in  a  volume  of  140  c.c.  of  0.7  M  sul- 
furic  acid  ;  the  aerated  solutions  were  cooled  to  room  tempera- 
ture before  titration.  These  results,  together  with  those  in 
Table  VII  are  considered  sufficient  to  disprove  the  prevailing 
notion. 

TABLE   VI. 

Time  for 

Oxidation  Temp,  during  Fe  titer 

No.                  Min.                     Oxidation  c.c. 

1  none                      18.32 

2  15  26°  -»22°  18.35 

3  15  90°— >48°  18.33 

4  30  100°-»36°  18.40 

Regarding  vanadium;  it  has  been  found  that  air  bubbled 
through  a  hot  solution  oxidizes  tervalent  vanadium  to  tetra- 
valence  but  has  no  further  effect,  tetravalent  vanadium  being 
stable  toward  atmospheric  oxidation  even  in  hot  18  M  sul- 
furic  acid  solutions. 

Therefore  air  passed  into  a  hot  acid  solution  containing 
ferrous  ion  and  tervalent  vanadium  should  convert  the  latter 
to  tetravalent  vanadium  but  have  no  effect  on  ferrous  ion. 
Accordingly,  solutions  containing  0.1  g.  of  iron  and  0.0018  g. 
of  vanadium  in  140  c.c.  of  0.7  M  sulfuric  acid  were  reduced 
hot  until  colorless,  whereupon  the  reductor  was  removed,  the 
solution  heated  to  boiling  and  air  passed  rapidly  into  the  solu- 
tion for  varying  periods  of  time,  the  temperature  being  allowed 
to  fall  during  the  reoxidation.  Table  VII  shows  the  results 
obtained  in  experiments  with  varying  reduction  periods,  vary- 
ing reoxidation  periods  and  varying  titration  conditions.  The 
average  deviation,  disregarding  the  varying  conditions  of  re- 
duction, reoxidation  and  titration,  is  about  2.5  parts  per  thou- 

19 


sand,  while  the  average  deviation  is  much  less  for  those  ex- 
periments where  conditions  were  practically  the  same.  The 
general  average  checks  the  value  obtained  with  the  zinc  reduc- 
tor  within  two  parts  per  thousand.  This  procedure,  then,  has 
been  adopted  as  the  one  best  calculated  to  give  the  iron  and 
vanadium  content  of  the  ore,  the  vanadium  correction  to  be 
determined  by  the  Campagne  method  as  described  above. 


No. 

17 

19 

17a 

20 

21 

22 

24 

26 

27 

28 

29 

30 


Time  for 

Time  for 

Reduction 

Oxidation 

Min. 

Min. 

70 

17 

135 

20 

65 

15 

60 

15 

95 

20 

120 

20 

90 

60 

115 

5 

95 

5 

60 

5 

70 

6 

155 

5 

TABLE    VII. 

Temp,  during 
Oxidation 

100°  -»  50° 
100°  -»  46° 
83°  ->52° 
100°-»54° 
100°-M7° 

100°-»31° 
100°  -»  70° 
100°  -»  72° 
74°  -> 57° 
66°-»5l° 
100°->70° 


titer 
c.c. 
29.43 
29.44 
29.42 
29.41 
29.54 
29.49 
29.53 
29.53 
29.591 
29.542 
29.692 
29.692 


Corrected 

forV 

c.c. 

28.85 
28.86 
28.84 
28.83 
28.96 
28.91 
28.95 
28.95 
29.01 
28.96 
29.11 
29.11 

28.953 


Note  1:    Titrated  hot  (40°— 50°),  adding  H3PO4. 
Note  2:    Titrated  hot  (40°— 50°),  no  H3PO4. 

Note  3:    Average  of  12  determinations  with  an  average  deviation  of  .07 
c.c. ;   mean  of  two  determinations  by  Zn  reductor  is  29.00  c.c. 
Unless  otherwise  specified  the  reduced  solutions  were  titrated  at  20°  to 
a  pink  color  permanent  for  at  least  1  minute. 

The  following  Table  VIII  shows  the  results  obtained  with 
iron  ores  containing  no  titanium  or  vanadium  and  with  a 
Bureau  of  Standards  Sample  No.  29,  containing  0.594%  Ti  and 
0.054%  V.  In  the  procedure  used,  no  attempt  was  made  to 
eliminate  titanium  by  reoxidation,  nor  to  correct  for  vanadium. 


20 


No. 

1 


3a 
3a' 
3b 
3b' 
12a 
12b 
12c 
12c' 
12d 
12d' 
12e 
12e' 
12f 
12P 
29a 
29a' 


Temp. 

20° 

hot,  cool 


TABLE   VIII. 

Iron 

Ores 

Time 

H2S04 

ZnR 

Min. 

Molar 

c.c. 

80 

.7 

33.42' 

33.32 

75 

7 

32.31 

32.25 

105 

1.4 

62.362 

120 

1.2 

" 

120 

1.2 

62.47 

135 

1.4 

" 

75 

1.7 

29.92 

105 

1.8 

29.81 

90 

.7 

29.91 

75 

.7 

" 

80 

.7 

29.89 

75 

.7 

" 

100 

.7 

29.96 

75 

.7 

" 

80 

.7 

30.10 

90 

.7 

" 

80 

1.5 

32.343 

80 

1.2 

" 

H.  R. 

c.c. 

33.38 

32.36 
62.40 
62.23 
62.55 
62.49 
30.01 
29.85 
29.84 
29.85 
29.91 
29.83 
29.94 
29.86 
30.05 
29.90 
32.37 
32.35 


Remarks 


Repetition  of  3a 
Repetition  of  3b 

Repetition  of  12c 
Repetition  of  12d 
Repetition  of  12e 

Repetition  of  12f 

B  of  S  Sample  Ore  29 

Repetition  of  29a 


Note  1 :    KMnO4  Solution  D,  1  c.c.  =  .00344  g.  Fe. 

Note  2:    KMnO4  Solution  E,  1  c.c.  =  .003465  g.  Fe. 

Note  3:  Theoretical  value  calculated  from  Bureau  of  Standards  certi- 
fied average,  corrected  for  Ti  and  V  (55.75%  Fe).  A  certified 
value  uncorrected  for  Ti  and  V  (55.83%  Fe)  corresponds  to 
32.39  c.c. 

Procedure  Recommended  for  Iron  Ores 

Dissolve  a  0.2-0.3  g.  sample  in  concentrated  hydrochloric 
acid  (13M).  Fuse  the  residue,  if  any,  with  potassium  pyro- 
sulfate,  dissolve  in  hydrochloric  acid  and  filter  into  the  main 
solution.  If  no  such  fusion  is  made,  add  5  c.c.  of  sulfuric 
acid  (18M).  (If  vanadium  is  present,  evaporate  to  about  50 
c.c.,  then  add  to  the  hot  solution,  permanganate  solution  until 
a  permanent  red  color  is  produced,  and  boil  down  to  a  volume 
of  30  c.c.  Add  sufficient  hydrochloric  acid  (13M)  to  reduce 
any  manganese  dioxide  or  permanganate,  then  an  excess  of 
10-30  c.c.  depending  on  the  vanadium  content.)  Evaporate  to 


21 


dense  fumes  of  sulfur  trioxide.  Cool,  add  50-60  c.c.  of  water 
and  heat  until  solution  is  effected.  Again  evaporate  to  fumes 
of  sulfur  trioxide,  cool,  and  take  up  in  water.  Dilute  to  the 
volume  desired  in  the  hydrogen  reduction  process,  and,  if  vana- 
dium is  present,  titrate  to  the  desired  color  point  with  0.013- 
0.020  M  permanganate  solution.  The  selected  color  should 
persist  for  at  least  one  minute.  Deduct  from  this  titer  the 
color  "blank"  and  calculate  the  vanadium  content  of  the  ore. 
The  uncorrected  titer  is  to  be  deducted  from  the  second  titer 
obtained  in  the  following  procedure : 

Reduce  the  titrated  solution  with  the  hydrogen  reductor 
with  a  volume  of  about  150  c.c.,  and  an  acidity  of  about  0.5  M 
sulfuric  acid  until  it  has  become  colorless  while  hot ;  then  cool 
rapidly.  When  the  solution  is  again  at  20°,  remove  the  re- 
ductor, washing  with  water.  If  vanadium  or  titanium  is  pres- 
ent, pass  air  into  the  hot  solution  for  at  least  five  minutes. 
Titrate  with  the  same  permanganate  solution  used  above  and 
deduct  the  first  uncorrected  titer ;  the  result  will  give  the  iron 
value  of  the  ore.  This  method  is  suitable  for  the  determina- 
tion of  iron  in  ores  containing  any  amount  of  titanium  and  as 
much  as  1  per  cent,  of  vanadium. 

Determination  of  Vanadium  in  Steels,  etc. 

In  steels,  vanadium  usually  occurs  in  amounts  from  0.1  to 
0.2  per  cent,  in  the  "vanadium"  and  "chrome-vanadium"  steels, 
and  about  2.25  per  cent,  in  certain  "chrome-tungsten-vana- 
dium" steels.  Accordingly  dichromate-vanadate  solutions 
were  made  up  to  represent  these  two  types  of  steels,  contain- 
ing about  0.02  g.  of  chromium  with  0.002  g.  and  0.009  g.  of 
vanadium  respectively.  Since  the  determination  of  chromium 
by  ferrous  sulfate-permanganate  titration  has  been  well  estab- 
lished, the  hydrogen  reduction  process  was  applied  only  to  the 
determination  of  the  vanadium.  It  is  possible  to  use  the  same 
solution  in  which  the  chromium  was  determined,  to  reduce  the 
ferric  ion  and  vanadate  ion  to  ferrous  ion  and  tetravalent 
vanadium,  titrate  with  permanganate,  and  deduct  the  perman- 
ganate titer  equivalent  to  the  total  iron  added  in  reducing  the 
dichromate.  It  is,  however,  not  advisable  since  it  would  in- 
volve deducting,  for  example,  20.0  c.c.  from  a  total  of  20.5  c.c. 

22 


to  get  the  vanadium  titer  of  0.5  c.c.  of  0.013  M  permanganate. 
Therefore  a  separate  aliquot  of  the  total  chromate-vanadate 
solution  must  be  used. 

Dichromate  solutions  at  20°  were  not  appreciably  reduced 
by  hydrogen.  If  hot  and  fairly  concentrated  however,  they 
were  reduced  rapidly  and  definitely  to  chromic  ion.  But  under 
these  conditions,  as  with  iron-vanadium  solutions,  it  was  found 
impossible  to  prevent  vanadate  ion  from  being  reduced  to  a 
mixture  of  tervalent  and  tetravalent  vanadium.  Since  rapid 
reduction  of  dichromate  ion  and  definite  reduction  of  vanadate 
ion  to  tetravalent  vanadium  were  simultaneously  unattainable, 
it  was  decided  to  achieve  the  former  object  in  the  reduction 
process,  then  to  reoxidize  any  tervalent  vanadium  that  may  be 
formed  by  aerating,  as  previously  done  with  the  iron-vanadium 
solutions.  Consequently,  as  before,  the  undesirable  reduction 
product  was  removed  simply  by  bubbling  a  rapid  stream  of 
clean  air  into  the  solution.  For  this  reoxidation  the  reduced 
solutions  were  heated  to  boiling  (100°),  and  allowed  to  cool 
in  the  air  current  to  about  50° ;  after  15  minutes  of  aerating, 
the  solutions  were  cooled  rapidly  to  20°  and  titrated  with  0.013 
M  permanganate  solution. 

The  reduction  procedure  was  varied  as  may  be  seen  in 
Table  IX,  but  in  all  cases  where  air  was  used,  the  amount  of 
vanadium  found  was  in  satisfactory  agreement  with  that  taken. 
The  lettered  numbers  refer  to  solutions  of  chromic  ion  and 
vanadate  ion  produced  by  titration  of  the  solution  used  in  the 
experiment  with  the  corresponding  number  unlettered.  For 
these  solutions,  conditions  may  be  varied  more  widely  since 
there  is  only  vanadate  to  be  reduced ;  these  solutions  represent 
steels  or  ferrovanadium  containing  no  chromium,  and  from 
0.2  to  2  per  cent,  vanadium. 

The  reduction  of  dichromate  ion  to  chromic  ion  was 
usually  completed,  as  indicated  by  the  disappearance  of  the 
orange  color,  in  from  30  to  40  minutes.  Most  reductions  were 
continued  for  some  time,  to  ensure  the  reduction  of  vanadate 
ion,  but  the  larger  reduction  period  requires  a  longer  time  for 
the  reoxidation  of  tervalent  vanadium.  From  Experiments 
No.  32  and  No.  34,  it  may  be  seen  that  when  complete  conver- 
sion of  dichromate  to  chromic  ion  has  been  effected,  the  vana- 

23 


date  ion  has  also  been  reduced  sufficiently.  By  comparing  the 
total  time  required  for  reduction  and  reoxidation  of  Experi- 
ments 30  and  32,  it  is  evident  that  the  procedure  in  Experiment 
32  decreases  the  time  required  for  the  whole  process  by  0.5 
hour. 

TABLE  IX. 


Oxida- 
—  Conditions  of  Reduction  —      tion 

H  SO 

Vol. 

Time 

Time 

V  taken  V  found 

Dev. 

No. 

M2olar4 

c.c. 

Temp. 

Min. 

Min. 

Grams    Grams 

Grams 

24 

.7 

130 

hot,  cool 

60 

15 

.0018        .0016 

—.0002 

25 

.7 

130 

n      a 

60 

20 

.0019 

+.0001 

24a 

.53 

170 

tt      tt 

30 

none 

.0026 

25a 

.53 

170 

«      n 

30 

17 

.0017 

—.0001 

31 

.64 

140 

hot 

60 

18 

.0018 

.... 

26 

.6 

150 

hot 

60 

17 

.0089       .0092 

+.0003 

27 

1.4 

130 

hot,  cool 

60 

15 

.0089 

.... 

30 

.6 

140 

«      a 

60 

30 

.0090 

+.0001 

32 

.6 

140 

"      " 

40 

17 

.0089 

.... 

33 

.6 

140 

" 

60 

15 

.0091 

+.0002 

34 

.6 

140 

"      " 

40 

16 

.0089 

26a 

.5 

180 

cool 

60 

15 

.0089 

.... 

27a 

.53 

170 

cool 

45 

16 

.0088 

-.0001 

28a 

.53 

170 

hot 

45 

15 

.0092 

+.0003 

30a 

.5 

180 

H 

30 

16 

.0088 

—.0001 

26b 

.5 

360 

" 

45 

17 

.0086 

-.0003 

27b 

.5 

360 

" 

60 

15 

.0090 

+.0001 

28b 

.5 

360 

" 

30 

none 

.0089 

.... 

29b 

.5 

360 

M 

30 

17 

.0085 

-.0004 

Note:  Average  deviation  is  .00013  g.  vanadium. 

Procedure  Recommended  for  Steels 

Dissolve  a  2  g.  sample  (for  vanadium  content  of  2%,  use 
1  g.)  in  1  M  sulfuric  acid.  Dilute  with  water,  heat  to  boiling, 
add  a  saturated  solution  of  sodium  bicarbonate  until  a  slight 
permanent  precipitate  is  formed,  then  5  c.c.  in  excess.  Boil 
for  a  minute,  then  filter  rapidly.  (The  filtrate  may  be  used  for 
the  determination  of  manganese;  to  recover  the  manganese 
occluded  by  the  precipitate,  dissolve  it  in  dilute  sulfuric  acid, 
add  sodium  bisulfite  solution  (saturated)  to  reduce  ferric  ion, 
boil  off  the  excess  sulfur  dioxide,  dilute  with  hot  water  and  re- 
precipitate  the  oxides  of  chromium  and  vanadium  as  before; 

24 


add  the  filtrate  to  that  obtained  above.)  Dry  and  ignite  the 
precipitate  in  an  iron  crucible.  Thoroughly  mix  with  it  about 
10  g.  of  sodium  peroxide  and  fuse  cautiously.  When  cool, 
leach  with  water.  Boil  the  solution  for  a  few  minutes  to  de- 
compose any  excess  peroxide ;  cool,  then  transfer  to  a  250  c.c. 
'volumetric  flask  both  solution  and  ferric  oxide  precipitate. 
Filter  through  a  dry  paper,  rejecting  the  first  few  cubic  centi- 
meters of  the  filtrate.  From  the  filtrate,  withdraw  100  c.c.  for 
the  determination  of  chromium  and  an  equal  portion  for  the 
vanadium  determination. 

Determine  chromium  by  the  ferrous  sulfate-permanganate 
method.1  In  spite  of  the  color  due  to  chromic  ion,  the  end 
point  in  this  titration  is  entirely  satisfactory,  the  violet  tinge 
due  to  the  mixture  of  pink  permanganate  with  green  chromic 
ion  being  perfectly  reproduceable ;  a  "blank"  for  the  selected 
color  point  should  of  course  be  made.  Here,  as  in  all  titrations 
where  tetravalent  vanadium  is  being  Oxidized  to  vanadate  ion, 
the  color  tends  to  fade;  the  color  point  selected  as  the  end 
point  should  persist  for  at  least  one  minute. 

For  vanadium,  dilute  the  second  aliquot  to  130-140  c.c., 
add  an  excess  of  5  c.c.  of  sulfuric  acid  (18  M)  and  reduce  hot 
with  the  hydrogen  reductor.  As  soon  as  the  color  indicates 
complete  reduction  of  dichromate  ion,  remove  and  wash  the 
reductor,  heat  the  solution  to  boiling  and  bubble  air  into  it 
for  at  least  15  minutes.  Then  cool  to  20°  and  titrate  with 
0.002  M  permanganate  solution. 

If  the  steel  contains  tungsten,  dissolve  it  in  nitric  and 
hydrochloric  acids  and  remove  the  tungsten  as  tungstic  acid 
with  or  without  the  addition  of  cinchonine  hydrochloride. 
Occasionally  this  precipitate  occludes  chromium;  therefore 
dissolve  it  in  ammonium  hydroxide  and  re-precipitate  with 
hydrochloric  acid.  Concentrate  the  filtrates,  reduce  the  solution 
with  bisulfite  solution  (saturated)  and  precipitate  the  oxides 
of  chromium  and  vanadium  with  sodium  bicarbonate  solution ; 
continue  as  described  above. 

Sulfuric-phosphoric  acid  solutions  of  sodium  tungstate 
were  reduced  at  80°-90°  with  the  hydrogen  reductor.  Al- 


1  Details  may  be  found  in  W.  Scott's  Standard  Methods  of  Chemical 
Analysis. 

25 


though  precautions  were  observed  to  prevent  reoxidation  by 
the  air,  the  extent  of  reduction  in  at  least  a  dozen  experiments, 
was  found  to  be  never  more  than  10  per  cent,  of  the  theoretical 
amount  for  tungsten  pentoxide. 

Molybdic  acid  solutions  were  found  to  be  reduceable  by 
the  hydrogen  reductor  but  the  extent  of  the  reduction  has  not 
been  ascertained. 

SUMMARY 

1.  A  reductor  has  been  devised  to  permit  the  use  of  the 
simplest  of  reducing  agents,  hydrogen,  in  quantitative  analy- 
tical procedures. 

2.  The  effect  of  this  reduction  process  has  been  ascer- 
tained for  ferric  ion,  titanic  ion,  vanadate  ion,  and  tungstate 
ion. 

3.  A  procedure  has  been  worked  out  which  permits  of 
the  determination  of  iron  in  ores  containing  as  much  as  40  per 
cent,  titanium  and  1  per  cent,  vanadium. 

4.  A  method  has  been  evolved  for  the  determination,  in 
the  presence  of  chromium,  of  vanadium  in  steels  containing 
4  per  cent,  chromium  and  from  0.2  to  2.25  per  cent,  vanadium. 

5.  The  effect  of  the  hydrogen  reductor  upon  molybdic 
acid  solutions  has  been  observed  but  not  definitely  determined. 


26 


BIBLIOGRAPHY 

1  Lundell  and  Knowles,  J.  A.  C.  S.,  43,  1560  (1921). 

2  Hillebrand,  "The  Analysis  of  Silicate  and  Carbonate  Rocks," 

U.  S.  Geol.  Survey,  Bui.  700,  p.  186. 

3  Wardlaw  and  Clews,  J.  C.  S.,  117  (T),  1093  (1920). 

4  Marchetti,  Zeit.  anorg.  Chem.,  10,  66  (1895). 
*  Denham,  Zeit.  phys.  Chem.,  72,  641  (1910). 
"Teletow,  Zeit.  f.  Electrochem.,  12,  581  (1906) 

7  Diethelm,  Zeit.  phys.  Chem.,  62,  128  (1908). 

8  Eggert,  Zeit.  f.  Electrochem.,  20,  370  (1914). 

9  Eggert,  loc.  cit. 
10Campagne,  Ber.,  36,  3164  (1903). 

11  Treadwell-Hall,  Quantitative  Analysis,  Fifth  Edition,  p.  665 

(1919). 

12  Baskerville  and  Stevenson,  J.  A.  C.  S.,  33,  1104  (1911). 


VITA 

James  M.  Hendel  was  born  in  Reading,  Pennsylvania, 
January  24,  1893.  He  was  graduated  from  the  high  school  of 
that  city  in  1909,  and  from  the  Phillips  Exeter  Academy  in 
1910.  In  1914  he  was  graduated  from  Princeton  University 
with  the  degree  of  Litt.B.  From  February,  1916,  to  June,  1917, 
he  pursued  courses  in  chemistry,  physics,  and  mathematics  as 
a  "special"  student  in  Columbia  College.  In  the  summer  ses- 
sion of  1917  he  began,  and  in  February,  1919,  resumed  his 
graduate  work  in  Columbia  University.  In  the  summer  ses- 
sion of  1920  he  acted  as  Assistant  in  Chemistry.  From  Octo- 
ber, 1921,  to  the  present  he  has  been  Instructor  in  the  Depart- 
ment of  Chemistry  of  Hunter  College  of  the  City  of  New  York. 


478723 

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